Offshore Cage Research Articles

Desarrollo de Indicadores de Sostenibilidad para la Maricultura del Ecuador

Aquaculture in Ecuador has had an important development, mainly related to shrimp and tilapia culture. These species have been traditionally produced in ponds built on land. The cultivation of aquatic species on land has a large social, economic, and environmental impact, since this activity occupies large extensions of land, usually on ecologically sensible areas. An alternative to increase aquatic production without increasing the use of land and causing a low environmental impact could be the production of fish and shrimp in offshore cages, adapting technologies already used with success in other places. The present paper analyses the situation of mariculture (the cultivation of fish and other aquatic animals in open sea) in Ecuador, as well as the development of sustainability indicators that will serve for the sustainable development of this sector in the country.

Mariculture-induced introduction of cobia Rachycentron canadum (Linnaeus, 1766), a large predatory fish, in the Tropical Eastern Pacific

The cobia Rachycentron canadum (Linnaeus, 1766) is a highly valued fish by aquaculture producers and anglers. In spite of its wide-ranging distribution in tropical and subtropical seas, this species was absent in the Tropical Eastern Pacific until recently. In 2013 the government of Ecuador allowed the cultivation of cobia in offshore cages and in April 2015 three cages were deployed in Ecuadorian waters of the Pacific Ocean (Jaramijo, Manabi). Cobias escaped from one of these cages in August 2015 and we present the first report of R. canadum in the Colombian Pacific coast, ca. 600 km from the Ecuadorian escape locality. This is the first report of its occurrence for the entire Tropical Eastern Pacific biogeographical region. Given its predatory nature, it is to investigate the potential ecological and socio-economic consequences of the introduction of the cobia in the region

The Efficacy of Inactivated Photobacterium damselae subsp. piscicida Combined with Levan/Alum as Vaccine against Photobacteriosis in Cobia, Rachycentron canadum

AbstractPhotobacterium damselae subsp. piscicida (Phdp) is a major pathogen of cultured cobia (Rachycentron canadum), a primary target species for offshore cage culture in Taiwan. Serum antibody titers as well as efficiency and duration of protection against Phdp were evaluated following intraperitoneal administration of a candidate vaccine prepared with formalin‐inactivated whole cells in combination with levan/alum adjuvants. The results showed vaccinates delayed the disease onset and had significantly (P < 0.05) less mortality than control nonvaccinates during Days 21–105 postvaccination with highest relative percentage of survival (RPS) and antibody titer up to 81.4% and 1:614, respectively. There was a highly significant positive linear correlation between the RPS and antibody titer (R2 = 0.841). Long‐lasting and significant protection against Phdp can be achieved with inactivated Phdp plus levan/alum, a potential cobia vaccine against photobacteriosis. Levan/alum complex may represent a promising adjuvant formula for the development of a Phdp vaccine.

Prevalence and survival of escaped European seabass Dicentrarchus labrax in Cyprus identified using genetic markers

The escape of European seabass Dicentrarchus labrax (L.) from fish farms is consid- ered to be a widespread problem in the Mediterranean area, where this species is produced in large quantities in offshore cages. Whilst estimates of the number of escaped seabass in the wild have been made previously, the actual distribution, long-term survival and the potential effects on native populations remain largely unknown. This study characterises the genetic profiles of all contemporary and some historic aquaculture sources of European seabass in Cyprus and uses these profiles to identify escaped fish in seabass collected from the wild around the island. Signif- icant differences in the microsatellite and mitochondrial DNA marker profiles were found between farmed and wild fish. The number of escapees identified was 15% of the total number of wild-caught fish sampled. However, escapees were not equally distributed; at one location ~70% of wild-caught fish were escapees while in other areas escapees only accounted for up to 4%. Escapees were present in all size classes of fish, but the majority were of commercial size (300�500 g) typical of seabass farmed in seacages. This indicates that they may have escaped recently and during normal aquaculture operations as no escape event was reported in the course of the study. Two large, egg-bearing females and some juvenile fish were also classified as escapees, which suggests that long-term survival and interbreeding with wild fish is possible in Cypriot waters.

Design of Remote Detection System for Mooring-Rope Force of Offshore Cage Based on Wireless Ad Hoc Network

In order to facilitate studying real-time mooring force of offshore cage, based on the combination of ZigBee and GPRS technologies, the secondary development was conducted, the detection system of mooring force was designed. It was mainly designed the overall system solution and integrate the system hardware architecture, the development of the software programs of analog-data acquisition, ZigBee networking, remote data transmission and the server were designed. The system test results show that the data could be effectively transmitted between the terminals and server. This system is small in size and low power consuming which can be used as a remote detection tool of mooring force in process when studying on offsore cage aquaculture.

First attempt to assess the viability of bluefin tuna spawning events in offshore cages located in an a priori favourable larval habitat

Most of the Atlantic bluefin tuna caught by the purse-seine fleet in the Mediterranean Sea are transferred alive into transport cages and towed to coastal facilities where they are fattened. This major fishery is targeting aggregations of reproductive bluefin tuna that continue spawning within the transport cages. Our study is the first attempt to assess the viability of the spawning events within transport cages placed offshore in a priori favourable locations for larval survival. The study was conducted in June 2010 in the Balearic Sea, a main spawning area for bluefin tuna in the Mediterranean. The location of two transport cages, one with wild and one with captive tuna, coincide with the situation of the chlorophyll front using satellite imagery as a proxy for the salinity front between resident surface waters and those of recent Atlantic origin. The results showed that bluefin tuna eggs were spawned almost every day within the two cages but few or no larvae were found. The expected larval densities estimated after applying mortality curves to the daily egg densities observed in the cages were higher than the sampled larval densities. The trajectories of the eggs after hatching estimated from a particle tracking model based on observed geostrophic currents and a drifter deployed adjacent to the cage suggest that larvae were likely to be caught close to the cages within the sampling dates. Spawning events in captive tuna in transport cages may hatch into larvae though they may experience higher mortality rates than expected in natural populations. The causes of the larval mortality are further discussed in the text. Such studies should be repeated in other spawning areas in the Mediterranean if spawning in cages located offshore in areas favourable a priori for larval survival is likely to be considered a management measurement to minimize the impact of purse-seine fishing on tuna.

Physiological Changes in the Red Drum after Long‐Term Freshwater Acclimation

The effect of long-term freshwater acclimation on the blood and plasma ion composition of Red Drum Sciaenops ocellatus was investigated with the goal of elucidating the necessity of ion remediation. Four replicates (n = 50) of freshwater-acclimated (FW) fish (1.6 ± 0.2 g) were raised in 25-m(3) tanks supported by 140,000 L of recirculating water. Four replicates (n = 50) of seawater (SW) fish groups were placed in 40-m(3) offshore cages at 32-35 psu. Blood was collected from 100 fish (FW = 578 ± 50 g; SW = 686 ± 45 g) of each group (FW, SW) after 8 months of rearing. During the grow-out phase, the survival of FW and SW fish was 57.5% and 92.2%, respectively. The water ion composition (mainly the Ca(2+)/K(+) [43%] and Ca(2+)/Mg(2+) ratios [1%]) explained 56.6% of the plasmatic ion variability in the fish groups. Freshwater exposure produced significant reductions in osmolality and in several plasma indicators (Na(+), Cl(-), and Mg(2+)); the K(+) levels from FW fish were the most compromised parameter. The water Ca(2+)/Na(+) ratio had a greater influence (44%) on the plasma chemistry parameters, mainly glucose and creatinine. Freshwater-acclimated fish had a higher percentage of hematocrit, hemoglobin, and red blood cells than SW fish, but the water quality explained only 12.5% of the blood parameter variability between the FW and SW groups. The results support the conclusion that Red Drum tolerates salinity variations and can adopt a relatively stable condition for short periods; however, the data suggest that Red Drum have only a limited ability to withstand a hyposmotic environment for long periods due to their limited ability in maintaining K(+) concentrations without external supplementation. Freshwater environments with high Ca(2+)/Na(+), Ca(2+)/K(+), and Ca(2+)/Mg(2+) ratios appear to be a chronic stress factor that should be considered in future experiments.

Blood Hemogram Profiles of Farmed Onshore and Offshore Gilthead Sea Bream (Sparus aurata) from Sicily, Italy

The aim of the present study was to assess the values of haematological parameters using an automatic method and to evaluate the blood profile in gilthead sea bream (Sparus aurata) reared in different aquaculture systems (offshore cage and onshore tanks). For this reason, 100 fish (5 replicates for each aquaculture system) reared in two Sicilian farms with different management: offshore cages (Farm 1) and onshore open concrete tanks (Farm 2), were used. In both aquaculture farms, physical and chemical characteristics of water were detected. After collection, blood samples were immediately analysed with both manual and automatic methods. Our results showed that sea bream with similar biometric data (in mean 292 g in weight and 27.2 cm in total length for Farm 1; 232 g in weight and 24.6 cm in total length for Farm 2), but rearing in different conditions, have different baseline haematological values and this underline that water quality could influence haematological parameters of fish. In particular, it was seen that Farm 2 showed a lower value of RBC, Hct and WBC and higher value of Hgb, TC, MCV, MCH and MCHC than Farm 1. In particular, mean values of 3.28 and 2.89 in RBC; 7.38 and 45.19 in Hct, 8.31 and 10.66 in Hgb, 62.55 and 53.80 in WBC, 67.92 and 88.66 in TC, 146.3 and 157.5 in MCV, 25.55 and 37.13 in MCH and 17.6 and 23.62 in MCHC were recorded respectively for Farm 1 and Farm 2. The variations in haematological parameters due to different location of farm allow us to claim that changes in blood characteristics are important indices in monitoring the effect of habitat changes and management on the fish physiology.

Designing offshore fish cages using systems engineering principles

AbstractThe human population reached 7 billion at the end of October 2011, accentuating the challenge to increase food production to meet the demand. Offshore mariculture, which does not depend on wild fish harvest, has the potential to become a primary food source to meet this demand. Despite an overall interest and justification in investments in offshore aquaculture, there are very few offshore cage designs suitable for use today. The goal of the current paper is to describe a research project that applied systems engineering principles to develop and document a set of requirements and identify the relevant technical components that are needed to design a sustainable offshore cage system. Requirements from the sector should be met by a robust environmentally friendly cage system ensuring the welfare of the fish and capable of producing a quality fish product demanded by the consumer. Future design work will build on the proposed preliminary architecture to satisfy these requirements. © 2012 Wiley Periodicals, Inc. Syst Eng

Seasonal screening of AChE, GSH and gonad histology, in European sea bass Dicentrarchus labrax L. reared in three different fish farms

The aim of this work was to do a preliminary seasonal screening of ecotoxicological biomarkers in European sea bass Dicentrarchus labrax in three different fish farms, to know if the different location and typology can discriminate them. A set of selected biomarkers of xenobiotic exposure, such as acetylcholinesterase (AChE) activity, Glutathione (GSH) and gonad morphology were investigated seasonally in male European sea bass D. labrax (L.) reared in three different intensive farms: a land-based farm of cement tanks (T), an in-shore sea cages farm (C1) and an off-shore sea cages farm (C2). The results showed that both location and typology can discriminate AChE activity, GSH content and gonad morphology. Further investigation is needed to propose these biomarkers in the protocol of fish farm quality control.

Do benthic biofilters contribute to sustainability and restoration of the benthic environment impacted by offshore cage finfish aquaculture?

Benthic biofilters were deployed under a cage fish farm and in two reference locations to assess the influence of the farm on the biofilters and the surroundings, as well as to verify the usefulness of this technology as a mitigation tool. The biofilters underneath the farm recruited a fouling community practically identical to that of the control biofilters, which included a variety of trophic strategies. The former showed a higher 15N enrichment, indicating that fouling beneath the farm was benefiting from the farm waste. The waste retention efficiency was low (0.02gNm−2month−1) beneath the farm. Benthic biofilters aggregated demersal wild fish around and within them. Pelagic wild fish also frequently used the biofilters beneath the farm, forming compact shoals around them. The increased complexity of the habitat below the fish farm enhanced biodiversity, but this improvement did not lead to the recovery of the sediments around the biofilters.

Evaluating the influence of off-shore cage aquaculture on the benthic ecosystem in Alghero Bay (Sardinia, Italy) using AMBI and M-AMBI

The impact of an off-shore fish farm in Alghero Bay (northwest Sardinia, Italy) on the benthic ecosystem was investigated in 2007 and 2008. In addition to studying the chemical and physical characteristics of the area (i.e., currents and sediment analyses), some biological analyses were also performed. The AZTI's Marine Biotic Index (AMBI) and the multivariate AMBI (M-AMBI) were calculated, which are being used in assessing the ecological status of benthic communities within the European Water Framework Directive (WFD). Clear impact gradients were detected according to both methods; they are related to farm production, prevailing currents, and characteristics of the area (i.e., water depth and distance to the cages). The site affected most was detected within 84 m from the cages; the area that no longer showed effects was over 907 m from the cages. The gradient is shown by decreasing AMBI values and percentage of opportunistic species and increasing richness, diversity, and the presence of sensitive species. This study highlights the importance of setting reference conditions for different areas when calculating M-AMBI. These reference conditions correspond to those in undisturbed sites in the opposite direction of the prevailing currents within the area.

Offshore Farming of the Mediterranean Amberjack (Seriola dumerili) in the Northeastern Mediterranean

The growth rate, survival, and feeding parameters of Mediterranean amberjack (Seriola dumerili Risso, 1810) cultivated in offshore cages in the Gulf of İskenderun (Hatay, Turkey) were investigated from July 2006 to March 2008. Two offshore cages (339 m3) were placed at a depth of 10 m in a sheltered area 500 m off the coast. Juveniles (101.97±14.54 g), caught with seine nets 400-1200 m from the coast, were stocked in the cages at 250 per cage. Fish in one cage, Group A, were fed commercial pellets for all 20 months whilst fish in the second cage, Group B, were fed pellets for the first 16 months and frozen sardines for the following four. The mean live weight, survival, feed conversion ratio, daily feed consumption, and water quality parameters were recorded monthly. Group B reached a significantly (p<0.05) greater weight (2785.00±64.91 g) than Group A (2441.14±38.13 g). Food conversion ratios ranged 1.16-2.46 for group A and 1.10-2.28 for group B, low when compared with other studies on amberjacks in the Mediterranean. Average mortality was 25%, due to a Zeuxapta seriolae (Monogenea: Heteraxinidae) infection in December 2006 (20%) and fish handling for measurement in June 2007 (~5%). The farmed amberjacks had significantly higher protein and lipid contents than their wild counterparts at the end of the 20-month feeding period. Amberjacks found frozen sardines more appealing than pellets, especially during the winter. In conclusion, it is advised to feed Mediterranean amberjack frozen sardines or other trash fish during the winter grow-out period. Their rapid growth rate, as well as their adaptability to farming, make offshore net cages a promising system for the aquaculture of this species.

Survey of qualitative traits of European sea bass cultivated in different rearing systems

AbstractThe purpose of this study was to evaluate the main qualitative traits of European sea bass fattened in farms adopting different rearing techniques (offshore cages, inshore cages, land‐based basins) but fed the same diets in each production cycle, in a three year survey (2006, 2007, 2008). Three farms were chosen for each rearing technique and two sampling sessions of ten fish each were carried out for each rearing cycle. Proximate composition, fatty acid profile, and cholesterol content were evaluated in the fillet of marketable size fish as well as morpho‐biometric parameters and indices. Diets administered in 2008 had higher amounts of lipids, lower proportions of n–3 polyunsaturated fatty acids (PUFA) and higher proportions of n–6 PUFA compared to 2006 and 2007 diets. The chemical and fatty acid composition of the fish fillet was affected by the diet composition: fish fattened in 2008 exhibited statistically higher amounts of fat and cholesterol, lower proportions of n–3 PUFA and higher proportions of n–6 PUFA in comparison with fish cultivated in 2006 and 2007. Fish cultivated in cages, both offshore and inshore cages, exhibited leaner fillets, lower amounts of cholesterol and higher proportions of n–3 PUFA than fish cultivated in basins.Practical applications: In this study we have analyzed the combined effects of feeding and rearing systems of sea bass in a 3‐year survey for the first time. The results showed that feeding is the main factor affecting fish quality as regards both the chemical composition and the fatty acid profile. The partial substitution of fish meal and fish oil with vegetable sources, with the aim of saving the wild fish biomass as well as formulating less expensive diets, strongly alters the fillet composition. We also showed that the rearing system of fish in offshore cages makes it is possible to obtain better quality products.

Economic feasibility of using offshore oil and gas structures in the Gulf of Mexico for platform-based aquaculture

Abstract The increasing global demand for animal protein is a major ecological concern due to its impacts on land use, climate change, global grain supply and fisheries. One method for harvesting animal protein is to grow marine fish. This is widely practiced in coastal environments, but also leads to environmental problems associated with habitat loss and nutrient loading. One alternative is to move marine aquaculture further offshore, away from coastal land-use conflicts and towards ocean currents, which can efficiently dispose wastes. This concept creates a logistical challenge, however, since operators have to transport large amounts of food, fish and fuel to and from offshore cages on a regular basis and in varied weather conditions. In this paper, we discuss the economic feasibility of using offshore oil and gas platforms as bases for open ocean aquaculture in the Gulf of Mexico. We develop net-present value models of a platform-based operation and describe sensitivity analysis of the model output. We conclude that offshore platform-based mariculture may be commercially viable under favorable assumptions, that its viability requires economies of scale and depends principally on the yield per unit of cage volume achieved. The limitations of the analysis are described.

Seasonal cycles and long-term trends in abundance and species composition of sharks associated with cage diving ecotourism activities in Hawaii

SUMMARYShark cage diving is both popular and controversial, with proponents citing educational value and non-extractive use of natural resources and opponents raising concerns about public safety and ecological impacts. Logbook data collected 2004–2008 from two Oahu (Hawaii) shark cage diving operations were analysed to determine whether such voluntary records provide useful insights into shark ecology or ecotourism impacts. Operators correctly identified common shark species and documented gross seasonal cycles and long-term trends in abundance of Galapagos (Carcharhinus galapagensis), sandbar (Carcharhinus plumbeus) and tiger sharks (Galeorcerdo cuvier). Annual cycles in shark abundance may indicate seasonal migrations, whereas long-term trends suggest gradual exclusion of smaller sandbar sharks from cage diving sites. Numerically dominant (> 98%) Galapagos and sandbar sharks are rarely implicated in attacks on humans. Negligible impact on public safety is supported by other factors such as: (1) remoteness of the sites, (2) conditioning stimuli that are specific to the tour operations and different from inshore recreational stimuli and (3) no increase in shark attacks on the north coast of Oahu since cage diving started. Tracking studies are required to validate logbook data and to determine whether sharks associated with offshore cage diving travel into inshore areas used for in-water recreation.

Growth and mortality of common octopusOctopus vulgarisreared at different stocking densities in Mediterranean offshore cages

Four ongrowing cycles of common octopus (Octopus vulgaris), each with two stocking densities, were carried out in an offshore area in order to evaluate the effect of the following variables on growth (G, % body weight day−1) and mortality (M, % day−1): weight (W, 0.5–3.0 kg), temperature (T, 14–26 °C), stocking density (SD, 6–46 kg m−3), size dispersion, expressed as coefficient of variation (CV, 13–42%) and significant wave height (SWH: 0.4–1.2 m). The assays were performed in an 8 m3 stainless-steel floating cage divided into two compartments of 4 m3 each. For the range of temperatures considered (14–26 °C), G depended significantly on T and SWH, with maximum G values being obtained at 18.5 °C and with an important negative effect of SWH. M depended significantly on T, W and CV, mortality being minimal at 18 °C. The two other variables had an antagonistic effect, mortality increasing with greater size dispersion – suggesting that animals should be graded throughout the process – although the effect diminished as the sizes increased. The results point towards two alternatives for the commercial ongrowing of octopus under the particular conditions of the present study: (A) two ongrowing cycles of 3.5 months to reach a final weight of 2.5 kg or (B) one 5-month cycle to reach a final weight of 3.5 kg.

Tendances pour la pisciculture européenne de demain: cages au large, systèmes en eau recirculée et systèmes intégrés

Over the last few decades, European fish culture was developed mainly as a intensive monospecific activity. In most countries, marine aquaculture cannot continue to develop on the shore line where it first settled due to high competition with other activities. It has now to move either offshore or into recirculation systems located in less occupied spaces. Fresh water availability and impact of fish production farms on the environment are strongly restraining the development of the activity, which is even declining in some countries such as France. Recirculation systems make it possible to decrease water consumption and facilitate waste treatment. Their economical feasibility is being demonstrated and they offer an alternative to developing fish farms. Whatever the rearing system, nutrients of feed are partially converted into fish flesh and most of them are thrown back as wastes into the environment. Integrated systems make it possible to convert such nutrients into algae, molluscs or fish and to release purified water. This article presents some aspects of the development of three types of rearing systems which are increasingly used in northern Europe: offshore cage culture, recirculation systems and integrated systems.

Cloning of peroxisome proliferators activated receptors in the cobia ( Rachycentron canadum) and their expression at different life-cycle stages under cage aquaculture

We present the cDNA sequences and tissue mRNA expression of peroxisome proliferator-activated receptor (PPAR) α, β and γ isotypes in the cobia ( Rachycentron canadum), a warm water pelagic fish that is becoming a fish of choice for offshore cage farming. RT-PCR and real-time PCR showed that PPARα mRNA predominated in red muscle, heart and liver whereas PPARβ was expressed mainly in liver and pyloric caeca. In contrast, PPARγ transcripts were detected in all of the tissues examined, with the highest level occurring in visceral fat depot. Our 52-wk time-series investigation showed that while the mRNA expression of PPARγ in the cobia was positively ( P < 0.05) related to its body lipid deposition, a negative ( P < 0.05) relationship was found between PPARα expression in the liver and body lipid deposition. There was a significant increase in body lipid deposition and hepatic PPARγ expression as the fish grew. The hepatic PPARγ expression could be a sufficient parameter describing the bodily expression of PPARγ because of its positive correlation with PPARγ expressions in all other tissues. These results showed that PPARγ and α played a pivotal role in the control of lipid metabolic and storage functions in the liver, muscle and visceral fat depot of the cobia.

Comparison between some procedures for monitoring offshore cage culture in western Mediterranean Sea: Sampling methods and impact indicators in soft substrata

Two sampling methods, an array of physical–chemical and biological indicators, and uni-multivariate statistical procedures were compared on the basis of sensitivity to detect any impact and cost-effectiveness criteria, applied to environmental monitoring of fish farming. Sampling was conducted in a western Mediterranean gilthead seabream ( Sparus aurata) and meagre ( Argyrosomus regius) farm (San Pedro del Pinatar, SE Spain). Both sampling methods (Van Veen grab vs SCUBA diving) provided similar results for all the parameters except redox potential. The most sensitive chemical parameters of the sediment were total phosphorus, total ammonium nitrogen and acid volatile sulphide, but the latter was the only one which correlated with the macrobenthic community structure. The application of univariate methods to biological indicators only showed a clear trend in two (AMBI and BENTIX) of the five indices used. Both biotic indices, although statistically correlated with the spatial pattern of the macrobenthic community, provided different quality status categorization that could lead to misinterpretation and so, validation in offshore conditions is required. Nevertheless, multivariate analysis of macrofauna confirmed a noticeable spatial pattern, at the same time that this statistical strategy has been proven and validated in a wide range of marine community studies.